Concrete arch construction



Maich 6, 1945. 5 WH Y 2,370,763

CONCRETE ARCH CONSTRUCTION Filed May 4, 1942 2 Shets-Sheet 1 INVENTOR. v

CAM WALL March 6, 1945. 4 Q 5 wHlTNEY 2,370,763

CONCRETE ARCH CONSTRUCTION Filed May 4, 1942 2 Sheet-Sheet 2 3w TELENJ, WWW/3 554 w 1W? Patented Mar. 6, 1945 UNITED STATES PATENT. OFFICE CONCRETE ARCH CONSTRUCTION Charles S. Whitney, Milwaukee, Wis. Application May 4, 1942, Serial No. 441,681

, 7 Claims.

This invention relates to reinforced concrete roof arches of the type in which spaced arch ribs are arranged to carry intervening roof slabs, and it resides in an improved form of such roofs in which the locus of attachment of the roof slabs to the arch ribs is disposed sufficiently near the neutral axis of the ribs to substantially reduce the contribution of stress from the roof slab material to the ribs or from the ribs to the roof slab upon flexure of the roof in response to loading and volume changes.

One of the objects of this invention is to provide a reinforced concrete arched roof which reacts with smaller thrusts when its extremities are displaced relative to one another, or which, when its extremities are restrained, imposes, smaller thrusts due to volume changes upon the restraining abutments.

Another object of this invention .is to effect a substantial saving in the quantity of concrete and steel required in an arched roof of a givensize.

Another object of this invention is to increase the distance which can be'economically spanned by a reinforced concrete arched roof of the type here involved. I

Another object of this invention is to substantially reduce the amount of cracking of the roof slab by reducing the amount of tensile stress which is imposed thereon. V

The above and other objects and advantages of this invention will appear from the description of the invention which follows.

Heretofore in the art, reinforced concrete roof arches which are restrained at their spring lines by abutments have been constructed to present either a smooth exterior shell or barrel, or a smooth interior shell or barrel, that is to say the intervening roof slabs have been secured to the arch ribs either at or near their upper or lower extremities. This practice has been detrimental to structural economy of such arches because it concedes little to the important fact that in a structure of this sort and of optimum economy a substantial measure of non-destructive yielding or elasticity must be preserved in the arch rib. This is because concrete is subject to substantial volume changes in response to alterations in ambient temperatures and moisture conditions. When these changes occur the thrusts in the arch change in much the same manner as they would change if" the abutments were moved toward or away from one another.

In structures of the type here involved reliance upon the tensile strength of theithln roof slab to contribute to the necessary load sustaining strength of the rib skeleton is not accepted as sound practice. While the strength contributing capacity. of the slab acting in tension must be ignored it is equally imperative that the compression sustaining capabilities of the slab be taken into account in determining the tension stresses which arise on bending in the parts of the ribs on the opposite side of the neutral axis. Thisis of importance because tensile stresses due to bending arising out of thrusts caused by volume changes increase with an increase in the moment of inertia of the section of the effective rib and this section must include not only the section of the rib itself but also the section of the adjoining roof slabs.

The stiffness of the rib, taking into account the effect of the roof slab is therefore greater than the stiffness which is credited to the rib for load sustaining purposes. From this it follows that an isolated rib in which the extremities are restrained by abutments and'which'is'designed for optimum economy is inadequate to sustain the thrusts due to volume changes when the roof slab is attached thereto in a position where the moment of inertia of the effective rib section is largely augmented. The problem created'by this relationship has heretofore been dealt with by disposing suflicient material, in the partof the rib on the side of the neutral axis opposite the slab, to hold the tensile stresses in the rib within safe limits. This adds further'to the stiffness of the arch and in arches, the extremities of which are restrained, the thrusts against the abutments due to volume changes are increased accordingly.

This in turn calls for stronger abutments and entails more elaborate footings and foundations designed to provide for an inevitably increased measure of foundation yielding. I

In contrast, I have discovered that the roof slab may be attached to the rib at'or near the neutral axis of therib-and when this is done the moment of inertia of the effective rib section is little different from that of the rib alone and little or no material need be added to the rib to withstand the augmentation of the thrusts due to volume changes which become efiective upon attaching the slab. The savings thus efiected'may amount to a very considerable part of' the material required for any given structure. This saving extends not only to the ribs but also to the abutments and foundations and is accentuatedin arch roofs of large span such as may be used for sports arenas. airplane and airship hangers, public meeting halls and the like. Not only is a savingpin material made possibleby this invention but the distance which may be economically spanned by a reinforced concrete arch roof has been increased and cracking of the roof slab has been reduced through its application.

This invention is herein described by reference to the accompanying drawings which form a part hereof and in which there is set forth by way of illustration and not of limitation one conventionalized instance of a structure embodying this invention.

In thezdrawin'gsr Fig. Us a perspective view, partly broken away, of a building constructed in accordance with this invention;

Fig. 2 is a detailed sectional viewin side'eleva tion, viewed through the plane 2-2,,indicated in Fig. 1; and,

Fig. 3 is a detailed sectional view in frontele'va-- tion viewed through the plane 33, indicated in Fig. 1.

The structure illustrated in Fig. 1-,. represents an. instance ofthis invention embodied in the side-wallsandmoof porticnsbf a conventionalized building, although. the. invention is. adapted to structural: shells-of. awide variety of forms In the. structure shown, a plurality of spaced, paralle1.arch ribs I, spring from rigidly fixed abutmentsformed from vertical columns 2 andv struts or buttresses 3. The columns 2, and the but tresses 3 extend below ground level torapprcpriate footings :not shown. The arch ribs I are thus restrained: by the abutments and thereforv must fiexin response to volume changes caused by thermal expansion, moisture changes, shortening under load and similar effects. The ribs 1 as shownas well as the co1l1mns2 and buttresses 3 are: made up of. concrete reinforced by steel located and proportioned as shown or in any suitable manners Disposed between the ribs l and secured thereto are roof slabs 4. The slabs 4 are also made up of reinforced. concrete which may be. poured inte'grally with the ribs as shown or may be separately formed and secured t the ribs in any convenient manner. The. slabs 4 are locatedwith respect to the ribs: I at a zone which embraces the cylindrical surfacedefinedby the. neutral axis of: theribs L This clearly appears in they two detailedsectional views,,Figs. 2 and 3. By thus locating theslabs 4, which are much thinner than thevertical. dimension of the ribs; the capacity of the ribs l to flex-in a vertical directionislittle afiectedi Fromthe above it will be-seen that when slabs are secured toribs as they are in prior structures-at-either theupper or lower. extremities of the ribs the" effective rib is greatly stiffened as compared with the structure of this invention and the stress. in the portions-of the ribsremote from the slabs. is greatly augmented for any given amount of deflection in the roof, Since the amounts of such deflections are fixed by the physical constants. of. the concrete such as, its coefiicient of thermal expansion and the like, the increasedstiiinessin the rib cannot act to diminish the deflection to any appreciable extent. As aresult higher thrusts and higher stresses resultingfrom volume changes are inevitable. The novel roof structure of this invention, however,

avoids these augmented stresses by; locating the roof. sl'abs-timthe vicinity of the. neutral axis of therib. When this is dcnethelmoment oi inertia of: the section. of the efiective. rib is-very little greaterthani that of theribitself. This is particularly true because the. depth of theslab is usually less than one fourth the depth of the rib. As a result the rib is free to act in bending much as though the roof slab were absent. This reduced participation of the roof slab in the bending action of the rib also is of marked advantage from the standpoint of the amount of tension cracking to be expected in the roof slab. With the slab located in accordance with this invention little tensile stress is imposed upon the slab upon bending of the rib,,and cracking from this cause: is practically: eliinihate'di.

By. constructing for greater flexibility rather than greater rigidity, the normal and expected course has been departed from in this invention and by following this contrary path a stronger and more economical structure is arrived at.

While this invention has been herein described by references toone specific instance of its embodiment it is intended that this instance shall not unnecessarily limit the protection to be afforded hereby, the intent being that. the protectionto be afiorded hereby shallextend to thefull limit of the inventive advance disclosed hereinas defined by the claims hereto appended;

I'clai'm:

1. In a. reinforced concrete. archedv roof, the combination comprising a plurality. of spaced parallel reinforced concrete. arch. ribs said. ribs having a cross section the. vertical dimension of whichis substantially greater. than the horizontal dimension thereof, a pair of restraining abutments for each rib anchored. against. outward movement whereby accommodation. for volume changes in the. material of the ribs. is. accomplished to a substantial extent -bybending. of said ribs, said abutments. being rigidly attached to said ribs, and reinforced concrete. roof slabs of arched configuration conforming. to thev curvature of said ribs disposed between.saidribs. and secured. thereto throughout the extent of said slabs at azone which embraces theneutral axis of said ribs, said slabs. having a thickness less than one fourth the vertical dimension. of the crosssect'ion ofsaidribs.-

2. In a reinforced concrete arched; roof, the combinationcomprising aplurality of spaced parallel curved reinforced concrete. arch. ribs, apair of restraining. abutment for 'ea-chrib anchored against outward movement whereby accommodation for volume. changes in. the material. of the ribs is accomplished to. a substantial extentby' bending of said ribs, andr'ooislabs of arched configuration conforming to thecurvature of. said ribs. disposed between said ribs and attached thereto throughout the extent. of said slabs along zones interme diate the. inner and outer faces. of said ribszin position to embrace the neutral axis-of said. ribs.

-3. In an arched roof. the. combinationcomprising a lurality of spaced parallel curved-arch ribs, a: pair'of. restraining abutmentslfor each rib'anchored against outward movement. whereby accommodation. for volume changes in thematerial of the ribs is accomplished. to a substantialeX- tent by bending of said ribs, and roof slabs. of arched configuration conforming. to. the. curvature of saidribs disposed betweensaidribs. and attached thereto throughout the. extent of said slabs along zones intermediatethe inner and outer faces of saidribsin positionto embracetheneutral axis of said ribs.

4. In a reinforced concrete. arched root; the combination comprising a.plurality of spaced lparallel'curved reinforced.- concrete. arch ribs;.a pair of. restraining: abutments for eachrib anchored against outward movement whereby accommodabending of said ribs, and reinforced concrete roof V slabs of arched configuration conforming to the curvature of said ribs disposed between said ribs and attached thereto throughout the extent of said slabs along zones intermediate the inner and outer faces of said ribs in position to embrace the neutral axis of said ribs.

5. In a reinforced concrete structure the combination comprising a plurality of arch ribs of reinforced concrete, abutments for said ribs an-' chored against outward movement whereby accommodation of volume changes in the rib material is accomplished to a substantial extent by bending of said ribs, anda roof shell disposedlbetween said ribs and secured thereto midway be-, tween the inner and outer faces thereof in position to embrace the neutral axis of said ribs.

6. In a reinforced concrete arched structure, the combination comprising a plurality of spaced parallel curved reinforced concrete arch ribs,'a pair of restraining abutments for each rib anchored against outward movement whereby accommodation for volume changes in the material of 'thelribs is accomplished to asubstantial extent by bending ofsaid ribs, and roof slabs of arched configuration conforming to the curvature of said ,ribs disposed between said ribs and attached thereto within that area of the ribs intermediate 'and upper and lower surfaces where said ribs are substantially free of deformation due to simple bending. l I

7. In a reinforced concrete arch structure a plurality of spaced parallel curved reinforced concrete arch ribs having a radial depth of cross section greater than the breadth thereof, a pair of abutments for each rib anchored against outward movement whereby accommodation for'volume changes in the material of the ribs igaccomplished to a substantial extent by bending of said ribs, and a roof slab of a depth not more than one-fourth the depth of said ribs of arched configuration conforming to the curvature of said ribs and disposed between the same and attached thereto within that area of the ribs intermediate and upper and lower surfaces where said ribs are substantially free of deformation due to simple bending. c

' CHARLES S. WHITNEY. 

